The present invention relates to structures capable of feeding sheet material while operations are performed thereon.
The invention relates in particular to a unit which is capable of being attached to an existing machine for feeding sheet material past a work station of the machine where operations are performed on the sheet material.
It is of course recognized that a sheet material must be fed properly with respect to a work station where operations are performed on the sheet material. For example, in the case of a sewing machine, the sheet material which is worked on must be fed properly with respect to the needle which reciprocates through the sheet material to form stitches.
However, in situations of this latter type, proper feeding of sheet material is not assured at the present time. This is particularly true of multiple layer sheet material. For example in a sewing machine it is common practice to attach by a row of stitches an upper layer of sheet material to a lower layer of sheet material. Generally there is no problem in connection with the feeding of the lower layer of sheet material inasmuch as the latter is directly engaged by the feed dogs of the sewing machine. However, the upper layer of sheet material which is to be attached by stitches, for example, to the lower layer of sheet material is not engaged by the feed dogs and thus can easily slip with respect to the lower layer of sheet material resulting in undesirable gathers forming either on the upper or the lower layer of sheet material. Conventionally, reliance is only made on the pressure of the upper layer against the lower layer by way of the force with which the presser foot urges the upper layer against the lower layer. However, such pressure is not adequate in most cases to maintain the two layers of sheet material stationary with respect to each other while they are stitched together.
These problems have been recognized, and attempts have been made to solve them. However, up to the present time a satisfactory solution to the above problems has not been achieved. For example, it has been proposed to apply a rotary feed roller to the upper layer of sheet material so as to feed the latter together with the lower layer, but because of unavoidable slippage in the drive which rotates such a feed roller, there is still for the upper layer a different degree of feed than for the lower layer, so that the above problems have not been adequately solved up to the present time.